In a powertrain for a hybrid electric vehicle (HEV), an internal combustion engine and one or more electric motor/generator units selectively operate individually or together to propel the HEV. Power output from the engine and the motor/generators is transferred through gearing in a multi-speed transmission to a final drive unit. The primary function of a multi-speed transmission is to regulate the speed and torque distribution in the powertrain to meet vehicle speed and acceleration requirements.
An electrically variable transmission (EVT) in particular provides a continuously variable speed ratio, and can provide a direct mechanical path between the engine and the final drive unit. An EVT can operate with engine operation being mechanically independent from operation of the final drive unit or in various mechanical/electrical split contributions to thereby enable one or more high-torque continuously variable speed ratios, electrically-dominated vehicle launches, regenerative braking, engine off idling, and multi-mode operation.
A typical multi-mode hybrid vehicle having an EVT uses a transmission controller to enable selection of multiple EVT modes, fixed gear modes, and a neutral mode or modes, with various torque transmitting mechanisms or clutches being selectively actuated to provide a smooth transition between the available driving ratios. A supply of pressurized fluid is provided to the EVT for controlled actuation of the various clutches and other hydraulic components, and to establish the different speed ratios within the internal gear arrangement. The pressurized fluid may also be used for such additional functions as cooling and lubrication, as is known in the art.
The various hydraulic subsystems of a power transmission can be controlled via an electro-hydraulic control module, or HCM. The HCM, in collaboration with an electronic control unit or ECU, regulates the flow of pressurized fluid for cooling and lubricating the transmission components, and the selective pressurization of the various torque-transmitting mechanisms to enable transmission shifting. The HCM engages/actuates or disengages/deactivates the various transmission subsystems through the manipulation of hydraulic pressure generated within the transmission oil pump assembly using a plurality of valves. The valves used in a conventional hydraulic control circuit commonly comprise electro-hydraulic devices or solenoids, spring-biased accumulators, spring-biased spool valves, and/or ball check valves. However, conventional valve configurations and control methodologies may be less than optimal when used with an HEV having an EVT.